Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump on the machine that provides pressurized fluid to chambers within the actuators. An electro-hydraulic valve arrangement is typically fluidly connected between the pump and the actuators to control a flow rate and direction of pressurized fluid to and from the chambers of the actuators.
Machine hydraulic circuits that fluidly connect multiple actuators to a common pump experience undesirable pressure fluctuations within the circuits during operation of the actuators. In particular, the pressure of a fluid supplied to one actuator can undesirably fluctuate in response to operation of a different actuator fluidly connected to the same hydraulic circuit. These pressure fluctuations may cause inconsistent and/or unexpected actuator movements. In addition, the pressure fluctuations can be severe enough and/or occur often enough to cause malfunction or premature failure of hydraulic circuit components.
One method of reducing these pressure fluctuations within the fluid supplied to a hydraulic actuator is described in U.S. Pat. No. 5,878,647 (the '647 patent) issued to Wilke et al. on Mar. 9, 1999. The '647 patent describes a hydraulic circuit having two pairs of solenoid valves, a variable displacement pump, a reservoir tank, and a hydraulic actuator. One pair of the solenoid valves includes a head-end supply valve and a head-end return valve that connects a head end of the hydraulic actuator to either the variable displacement pump or the reservoir tank. The other pair of solenoid valves includes a rod-end supply valve and a rod-end return valve that connects a rod end of the hydraulic actuator to either the variable displacement pump or the reservoir tank. Each of these four solenoid valves is associated with a different pressure compensating check valve. Each pressure compensating check valve is connected between the associated solenoid valve and the actuator to control a pressure of the fluid between the associated valve and the actuator.
Although the multiple pressure compensating valves of the hydraulic circuit described in the '647 patent may reduce pressure fluctuations within the hydraulic circuit, they may also increase the cost and complexity of the hydraulic circuit. In addition, the pressure compensating valves of the '647 patent may not control the pressures within the hydraulic circuit precisely enough for optimal performance of the associated actuator.
The disclosed hydraulic system is directed to overcoming one or more of the problems set forth above.